Integration of the electronic components such as semiconductors and increasing frequencies of operation clocks have been raising the heat produced by such components in recent years. Under such circumstances, maintaining temperatures at contact points of the electronic components within the range of the operation temperature has become a critical issue for the normal functioning of the electronic components. Increases in integration and frequency of the micro processing units (MPU) has been remarkable. Thus, dissipation of the heat produced by MPUs is particularly important for stabilizing their function and securing their operational longevity.
Heat emitted from the electronic components is, in general, dissipated by a cooling apparatus comprising a heatsink and a fan.
An example of a conventional heatsink will now be described referring to FIGS. 12, 13 and 14.
FIG. 12 shows a perspective view of a conventional heatsink. FIG. 13 shows a top view and sectional views of a conventional cooling apparatus. FIG. 14 shows a perspective view and a side view of another conventional heatsink. These heatsinks can be categorized into a plate-type heatsink where a plurality of plate fins 1c made of thin plates are disposed on a base plate 2b or a heat conduction section as shown in FIG. 12 (a), a pin-type heatsink where a plurality of fins 1 are disposed on the plate 2b as shown in FIG. 12 (b), and a tower-type heatsink where a plurality of plate fins 1c made of thin plates are disposed at right angle to the axis of column 2 as shown in FIG. 14 (a). These heatsinks are generally constructed of materials with high heat conductivity such as aluminum and copper, and produced by the extrusion molding (otherwise called pultrusion molding) method, the cold forging method, the die casting method, or the thin plates accumulating method.
The heatsinks are mounted either directly onto a heat producing element 3 as illustrated in FIG. 13 (a), or indirectly by inserting a heat diffusion plate 2c between the heat producing element 3 and the heatsink as illustrated in FIG. 13 (b) in the case of the pin-type heatsink. The heat diffusion plate conducts heat emitted from the heat producing element 3 to the heatsink, and helps to diffuse the heat and protect the heat producing element. The cooling mechanism of the cooling apparatus in use, is described as follows: heat produced by the heat producing element 3 is conducted to the pin-shaped fins 1 via the heat-conductive base plate 2b made of a highly heat conductive material such as aluminum, and, over the surface of the fins 1, convectively conducted to the air blown by a cooling fan 4 thus dissipated into the air and cooled.
In order to improve the capability of the cooling apparatus, heat is most desirably diffused throughout the heat conductive section evenly, and dissipated from all of the dissipation fins. However, in the case of the plate-type and pin-type heatsinks, heat emitted from the heat producing element 3 tends to be conducted intensively to the dissipation fins disposed right above the heat producing element 3. It is relatively hard for the heat to be conducted to the peripheral dissipation fins. The reason for this is that the heat producing element is much smaller than the heat conducting section, thus contact area between them is very limited. Consequently, with the plate-type and the pin-type heatsinks, the heat dissipation fins as a whole often fail to function effectively.
It could be argued that if the amount of air flow around the heat dissipation fins is the same, the heat dissipating capability can be increased by expanding the surface area by increasing the number of fins. In reality however, considering unit area, when the sectional area of the heat dissipation fins is increased, the area where air can flow into, such as an air flow area 7e (marked with diagonal lines in FIG. 13 (a)) decreases, as does the total volume of air flow. Therefore, in some cases, the heat dissipation capability lowers as a result. In other words, a mere increase in the number of dissipation fins does not bring about an improvement.
The most important aspect for the dissipation of heat is to effectively conduct heat produced by the heat producing element 3 to the dissipation fins to the largest possible area.
To solve the foregoing problems the tower-type heatsink shown in FIG. 14 has been introduced. In this kind of heatsink, heat produced in the heat producing element is conducted directly to the upper part of the heatsink by a central column, and spread flatly by the plate fins 1c formed at a right angle to the axis of the column. The heat which has been spread flatly on the both faces of the thin plates is generally dissipated into the air by natural air cooling. In this tower-type heat sink, improvements have been proposed to increase the dissipation capability. For example, Japanese Patent Laid Open Publication No. S62-182600 discloses a heatsink where through-hole vents are formed on the surface of the thin plates by cutting and standing the cut edges of the thin plates in the process of producing the plate fins. Through these vents, air is permitted to convect more easily in the direction parallel to the axis of the column.
However, development of electronic components used in high speed processing such as semiconductors has been resulted in a relative increase in the amount of heat produced. As a result, conventional cooling apparatus are now facing difficulties in cooling electronic components sufficiently, especially when it comes to electronic components such as MPU which produce significant amount of heat, the conventional cooling apparatus fail to reach their full capability. In some cases, temperature rise in MPUs led to thermal runaway and caused electronic apparatus to malfunction. To deal with increases in heat generation, it is possible to enhance the cooling capability by making the cooling apparatus itself larger. However, the size of the electronic apparatus itself inevitably limits the size and weight of the cooling apparatus.
Compared with other types, the construction of the tower-type heatsink realizes a better heat conductivity, however, it also tends to trap air. Furthermore, it is difficult to dispose a cooling fan on the top of the tower-type heatsink, therefore, the cooling fan must be disposed on a side face of the heatsink. However, if the cooling fan is disposed in such a manner, the heatsink is required to be as high as the cooling fan. Thus, the cooling apparatus as a whole becomes remarkably large. Despite its size, however, the dissipation efficiency can not be improved satisfactorily.
The present invention aims to address the foregoing problems, and to provide a compact and highly efficient heatsink and a small cooling apparatus with high cooling ability using the heatsink. The present invention further aims at providing a manufacturing method of the heatsink which achieves the production of a highly effective heatsink in a productive and inexpensive manner.